Leaf spring



Nov. 25, 1941. K. K. PROBST LEAF SPRING Filed July 29, 1939 a r/i L kjigi ATTORNEY.

Patented Nov. 25, 1941 UNITED STATES PATENT OFFICE LEAF SPRING Karl K. Probst, Detroit, Mich.

Application July 29, 1939, Serial No. 287,285

2 Claims.

This invention relates to a seat construction designed particularly for use in automobiles, although applicable to a variety of other uses, and has for its primary object to provide a seat which will give improved riding comfort at lower cost. In respect to this main object the present invention is similar to the inventions disclosed in my applications Serial No. 237,596 filed October 29, 1938. Serial No. 241,909, filed November 23, 1938, and Serial No. 242,684 filed November 28, 1939, which latter became Patent No. 2,202,301 issued May 28, 1940.

In the manufacture of automobile cushions, several important characteristics of design must be taken into consideration. For example, the cushion must deflect a substantial amount under the static loading of an occupant in order to give a sensation of softness; it must deflect substantially whether the occupant be a small, light weight person or a large, heavy person; it must not bottom under expected road shocks; it must be sufliciently soft for comfort during short occupancy and at th same time it must be sufficiently stiff to be restful after a long period of occupancy; it must be substantially form-fitting to an occupant and at the same time sufficiently stable to withstand pressures imposed by entire leg weight on the forward edge or pressure imposed during braking, both of which tend to roll the top of the cushion forwardly; it must have low rebound and damping characteristics; and, if it is to be built at lower cost, generally speaking, it must be of lighter weight. An object of the present invention is to provide a leaf spring construction for use as the springing medium for a seat cushion which embodies all of these characteristics.

More particularly, it is an object to provide a leaf spring construction in which the stresses are controllable and which, therefore, can be made to conform to a given set of deflections with the stresses equalized or coordinated with said deflections throughout the length of each leaf. It is found that, without special design, portions of the length of the springs are materially understressed and that by thus equalizing the stresses a material saving in weight results. In this respect. as will be hereinafter more fully explained, the front loops, the rear loops and the intermediate or bridge portion are formed as separate elements, and are of stock of graded thickness, selected to give the effect of localized stiffness. By fabricating the spring of portions of stock having graded thickness a saving in weight is effected because each portion is selected to work under uniform stress with the others.

In my co-pendlng applications above referred to the bridge portion is composed of a multiplicity of spring leaves in order that in a spring having sufficient softness at each end the center or bridge portion will have sufficient strength to carry the load. With the present arrangement, a single leaf of heavier stock is used. Whereas in the previous arrangement the stress in the center portion was too low for eflicient use of the material, due to the use of two or three thin leaves, the present invention uses a. single thicker leaf which provides the desired stifiness.

With the single leaf the stress though higher V is entirely within safe limits, and affords a material saving in weight.

Fabrication of the spring from a plurality of separate elements secured together has an important advantage from a manufacturing standpoint. In producing a spring from a single piece of mill stock it was necessary to form the center section from pretempered stock, and the necessity of using high temperatures to form looped end portions resulted in center warpage.

Another object is to provide for variation of the length of the spring without alteration of the end portions. According to this object production of the end portions is standardized and the length of the center sections vary, thus making alteration in the length possible simply by changing the length of the center section.

Another object is to provide an arrangement of the end and center sections which enables changing of the section modulus, to permit the top or center portion to conform to the shape of the body of the occupant. The usual tendency is to concentrate the weight on the end of the spine and the back of the knees, whereas the present arrangement enables support along the legs. The bottom of the leg, in sitting position, is essentially straight. and the front portion of the center leaf is attached to the front loop to provide a free portion which extends approximately horizontal. The center portion of the main loop tray bow while the horizontal front end provides yielding support for the leg back of the knee. independently of the action of either the center leaf or front loops. In other words. the forward edge of the seat gives a sensation of softness without altering the characteristics of the spring portions, thereby providing a soft effect when the body is shifted forwardly in lounging position, or when contacted by a person entering or leaving the automobile.

Another object a toprovide damping. or, in other words. a reduction in the number of oscillations following a deflection. In this respect, the

rear loops of the springs are connected by a flexible transverse member. and the back cushion is positioned so that it lightly contacts the seat cushion. In some cases either method of damping may be employed, or both might be employed together, according to the extent of dampingdesired.

Another object is to provide a sectional frame enabling assembly of the back cushion and the also 'for securing the upholstery or covering material in place.

Other objects and advantages will become more fully apparent as reference is had to the accompanying drawing wherein my invention is illustrated. and in which:

Fig. 1 is a vertical section of the assembled seat.

Fig. 2 is an elevation of theframe, with a portion thereof broken away and in section,

Fig. 3.is a section illustrating modification of the telescoping frame parts,

Fig, 4 is an exploded view of a spring,

Fig. 5 is a fragmental elevation illustrating the spring and upholstery anchoring means,

Fig. 6 is a fragmental elevation illustrating an exaggerated variation in thickness of the spring portions,

Fig. 'l is a fragmental elevation illustrating the free end portion of the main leaf in spaced relation to the front loop, and

Fig. 8 is a fragmental perspectiveview illustrating the damping means.

More particularly, I designates a seat cushion frame and 2 a back cushion frame, both frames having tubular upright portions 3. A tube or rod 4 is secured in one of the portions 3 with its end projecting therefrom, and the portion 3 of the other frame is adapted to be slipped thereover and subsequently secured thereto as by welding. In Fig. 3-, the seat frame member 3:: has a reduced end portion I adapted to extend into the tubular end 6 of the back frame member 2a,

and which is welded therein.

As will become more apparent from the following description, the two-part frame above described enables independent assembly of the seat and back cushions and subsequent placement of the cushions in proper relationship by telescoping'movement of the frame parts. This enables assembly of they back cushion in contact with the seat cushion to provide for damping.

As shown in Fig. 4, the seat springs are composed of three separate-parts, the front loops 1,

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course. and might be varied considerably under conditions different from those here contemplated. Fig. 8 emphasizes, however, that the center leaf is of stock heavier than that from which the end portions are formed.

With the center leaf formed of normally' straight stock. andheld in a bowed condition by attachment to the e'nd loops, the spring may be constructedto provide a high degree of softness at the front edge of the cushion, without changing the deflection characteristics of any part of the spring. This is illustrated in Fig. 7, wherein the center leaf is is attached to the front loop formation la remote from its end H, with the result that the end portion ll extends tangentially from the top, curved portion of the loop la. The end portion ll constitutes a spring whose function is independent of the loop formation In or the center leaf 9a.

The seat frame I embodies fore and aft transverse members l! having spaced sets of apertures l3, and the loop portions I and 0 have their terminal portions It shaped to embrace the frame members and provided with fingers II which extend into the apertures IS. The terminal portions of the spring members ar also formed with integral prongs I 6 which serve to retain the upholstering fabric i1 and padding material I! on the springs.

In order to provide for damping, a strip II is secured to the several rear loop formations I and connects the several springs together so that each offers modifying influence on the others.

The back cushion is similar in the respect that the springs 20 are fabricated in a manner similar members 2| in similar manner and have prongs 22 for holding he upholstering material 23 and padding 2| on the frame.

After assembly of the seat and back cushions on their frame sections I and 2, the frame sections are secured together insuch manner as to cause the lower edge of the back cushion to contact the seat cushion at 25. This provides for further damping, or supplements the damping acvtion of the strip It. It is contemplated, however, that the two metohds of damping may be used alternatively.

What is claimed is:

1. The combination of a frame and a plurality of parallel springs, each spring comprising front and rear portions each of multiple loop formation, a separate center leaf connected at its opposite ends to said front and rear portions, the terminals of said front and rear portions being bent to partially encircle portions of said frame, said terminals having integral lingers thereon adapted to extend into apertures in said portions of said frame to retain the bent portions on frame members, and said terminals havin inof parallel leaf springs,-the ends of said springs being bent to partially encircle portions of said frame, said ends having integral fingers projecting into apertures in said frame portions and having integral prongs for securing upholstery on the frame.

KARL K. PROBBT. 

